Enhanced Photocatalytic Performance of Halogenated Phenylacetylene-Decorated Cu2O Surfaces via Electronic Structure Modulation: A DFT and Experimental Study

This study investigates the photocatalytic performance of Cu₂O surfaces modified with halogen-substituted phenylacetylenes (4-XA), including 1-ethynyl-4-fluorobenzene (4-FA), 1-chloro-4-ethynylbenzene (4-CA), and 1-bromo-4-ethynylbenzene (4-BA), using an integrated theoretical and experimental approach. Through density functional theory (DFT) calculations and ultraviolet photoelectron spectroscopy (UPS) measurements, we analyze how these molecular decorators affect charge transfer dynamics and the electronic structure of the Cu₂O {100}, {110}, and {111} facets. Two distinct photocatalytic mechanisms are proposed: one where electrons reach the vacuum level through the molecular decorator and another where electrons escape directly through the Cu₂O surface via molecular-induced hybridized states. Our results show that 4-BA-modified {100} surfaces exhibit the strongest enhancement, which is attributed to the presence of in-gap molecular states, increased charge separation, and a significantly reduced work function. Experimental degradation of methyl orange validates the trend 4-BA > 4-CA > 4-FA, consistent with theoretical predictions. These findings highlight the crucial role of band structure engineering and provide guidelines for the rational design of high-performance molecularly decorated photocatalysts.